the registry in your container MUST talk to the EDb at least once. there is a cache for subsequent connections.. it will expire at some time, I don't know what the timeout is myself (never paid attention)..
but to get running, the Registry MUST contact the EDb on the 1st startup. if, like my environment, you start and stop containers of short duration, then they need to connect.
AND, with DT V9.1, the ability to cleanup the DB of transient registry entries has been removed.. so it will get cluttered pretty quickly.
CA doesn't understand this usage model yet. they assume that the services will be stood up, and long running
net, you need to find a communication path for these containers